1. Field of the Invention
The present invention concerns a nitrogen fireable non-oxidizing copper, easily solderable thick film conductor.
2. Background Information
In the hybrid microelectronics industry there is great impetus to develop base metal conductor inks. In contrast to noble metals, copper not only reduces the cost, but has better electrical properties than most of the precious metal counterparts. The adoption of copper has been slow for a few reasons, namely, availability of compatible resistors, the need for new capital equipment investment and difficulty in processing. This invention addresses the latter of these points.
U.S. Pat. No. 4,514,321 and U.S. Pat. No. 4,540,604 to Siuta discusses copper compositions that include reducing agents for copper oxide.
U.S. Pat. No. 4,072,771 to Grier, Sr. concerns a conductor composition that relies on preoxidized copper particles.
U.S. Pat. No. 4,323,483 to Rellick relates to fritless copper conductor compositions that are useful for forming microwave conductors.
U.S. Pat. No. 3,988,647 to Bolon et al discloses a copper conduct composition that uses oxide-free copper particles.
U.S. Pat. No. 4,070,518 to Hoffman is directed to a copper conductor which contains a frit which is lead-free and bismuth-free.
U.S. Pat. No. 4,172,919 to Mitchell relates to copper conductors with high bismuth-containing glasses.
Japanese 62-2405 to Matsushita Elec. Ind. KK discloses thick film copper conduct compositions which include copper powder, manganese oxide, copper oxide and glass.
U.S. Pat. No. 3,929,674 to Patterson concerns noble metal (Pt, Pd, Au, Ag) thick film conductor compositions with improved properties when containing aluminum boride and/or other borides or silicides.
U.S. Pat. No. 4,090,009 to Horowitz concerns electrical conductors made with Pd/Ag, and an inorganic binder. The binder must be free of bismuth oxide to reduce staining at conductor/resistor interfaces.
U.S. Pat. No. 4,001,146 to Horowitz relates to electrical conductors containing (a) metal powder comprising silver or a mixture of silver with Pt, Pd, Au or an alloy of Cu with one or more of Pt, Pd, Au and Ag and (b) a glass-free inorganic binder containing bismuth oxide and oxides of copper and/or lead.
U.S. Pat. No. 3,881,914 to Heiderlberg concerns the use of a phosphate-containing acid as a reducing agent for copper oxide.
Heretofore, there has not been a copper conductor having simultaneously the properties of good adhesion, good solderability and good conductivity even after multiple firings, with the additional property of being non-oxidizing.
As a fired conductor awaits further processing its surface usually changes due to environmental conditions, i.e., oxidizes. This can cause problems in subsequent operations such as soldering and ultimately component attachment.
Heretofore, expensive precious metals were used instead of copper because such metals do not suffer from oxidation after a short period. Alternatively, when copper was used, it had to be processed very quickly.